Study On The Application Of Quaternary Ammonium Gemini Surfactant And Its Clay Composite In Algae Removal Of Polluted Freshwater

In recent years, harmful algae blooms (HABs) which caused by eutrophication occurred more frequently in the lake of China. The outbreak of cyanobacterial blooms could cause great harm in a short time. Microcystis aeruginosa (MA) is one of the dominant cyan bacterial species. The excessive growth of toxic MA greatly deteriorated the water quality, damaged lakes’natural functions, and even threatened the drinking water resources. Therefore, to make safe, efficient and economical method is particularly important. In this dissertation, we employed Gemini surfactants and Gemini surfactant/clay composite to removal MA and discussed the mechanism of removal MA using Gemini surfactant and Gemini surfactant composite clay. The main research topics are as follows:1. Five kinds of quaternary ammonium surfactants, dodecyltrimethylammonium bromide (DTAB), cetyltrimethylammoniumbromide(CTAB),hexanediyl-1,6-bis(dodecyldimethylam-moniumbromide)(12-6-12), hexanediyl-1,6-bis(tetradecyldimethylammoniumbromide)(14-6-16) and hexanediyl-1,6-bis(cetyldimethylammoniumbromide)(16-6-16) were employed to remove Microcystis aeruginosa. In the same dosage, it was found that the Gemini surfactants show more efficient than single chain surfactants. Gemini surfactants with longer alkyl chain possess higher algae removal efficiency. The best dosage of16-6-16is20mg/L at the MA concentration of6.73×109cells/L. The effect of cell concentration, pH, water temperature, and ionic strength on the removal efficiency of MA cells was studied by employing Gemini surfactant (16-6-16) of the highest removal efficiency as algae remover. We used the zeta potential and microscopy to study the mechanism of16-6-16effect on MA.The results showed that the removal efficiency firstly increased and than decreased as the cell concentration increased.16-6-16had high removal efficiency when water temperature between15℃and25℃, but dropped beyond25℃. It is more suitable to alkaline freshwater than seawater.2. We combined16-6-16with natural bentonite to remove MA. And we also systematically studied the effect of the addition sequence (16-6-16and bentonite), water temperature, pH, clay particle size, ionic strength, and growth phase on algae removal efficiency. The optimal dosage of16-6-16and bentonite were obtained. The change of turbidity and chlorophyll a were employed to value algae removal effiencies. The results showed that the highest efficient is obtained by adding150mg/L bentonite first, and then adding7mg/L16-6-16after3minutes. Under this condition, the removal efficiency of chlorophyll a and turbidity can exceed90%after30minutes, which lead to a higher density floc. Our method of combining16-6-16with bentonite to remove algae was proved to be effective under variable conditions (temperature, growth phase, clay size). It is more suitable to alkaline freshwater than seawater.3. The results of microscopy observation, zeta potential and scanning electron microscopy measurement proved that netting and bridging is the main mechanism of removing algae by Gemini surfactant/clay composite.